inside os x Terminal window, typing this:

theserver:~ me$ defaults write -g AppleICUTimeFormatStrings -dict-add 2 "d MMMM y, HH':'mm':'ss z"

theserver:~ me$ killall SystemUIServer

…gets you this:

Tue 30 May 2006, 18:16 PDT

i prefer PST to PDT, so i'll prolly get rid of the wee 'z'.  btw, do not do 'Z' or 'ZZ' or 'ZZZ'.  bad things happen.